This invention relates to an ion source, specifically an ion source for use in an ion implanter for implanting ions in a substrate.
In manufacturing semiconductors through ion implantation several types of ion sources are typically used. Ion implantation requires ion sources with long operational life and high ion source efficiency. One ion source used in ion implantation is the Bernas type ion source which has been widely accepted in ion implantation.
FIG. 1 shows a top view of a single filament Bernas type ion source 1 with its top plate removed. Ion source 1 has a cathode 12 connects to a power source that drives cathode 12 to therminiocally emit electrons. Walls 14 of ion source 14 are biased relative cathode 12 so as to act as an anode. A repeller plate 18 is positioned behind cathode 12 and another repeller plate 16 is positioned across from cathode 12. The ion source is placed in a uni-directional magnetic field, as shown in FIG. 1.
During operation, a gas to be ionized is discharged into the chamber and is ionized by electrons emitted from cathode 12. Repeller plates 16 and 18 reflect primary fast electrons emitted from cathode 12 and generate an oscillatory electron movement along the axis of the magnetic field. In this manner, a plasma is generated in the ion source between cathode 12 and walls 14 for extraction by an extraction electrode outside ion source 1.
When the ion source operates, material such as vaporized metal from cathode 12 are deposited and sputtered on walls 14 and create a film on walls 14. Because this material is usually adhered weakly to walls 12, it can generate particles and file-flakes which in turn can short out the cathode and anode, for example, by resting acrose insulations 18.